A method of processing electrophysiological signals includes: receiving, over a limited time duration, sample electrocardiography (ECG) signals indicative of heart pulsatile activity occurring with a variable heart rate, wherein receiving the sample ECG signals is discontinued at an expiry of the limited time duration; receiving photoplethysmography (PPG) signals indicative of the heart pulsatile activity; determining a correlation between the sample ECG signals and the PPG signals; determining reconstructed ECG signals from the PPG signals as a function of the correlation between the sample ECG signals and the PPG signals; and estimating a heart rate variability of the variable heart rate as a function of the reconstructed ECG signals.